How Are Diameter, Aperture, and Focal Length of Lenses Related?

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SUMMARY

The discussion clarifies the relationship between diameter, aperture, and focal length of lenses. The diameter of a lens is the measurement across its circular edge, while the aperture refers to the opening that allows light to pass through, which can be equal to or smaller than the diameter. The focal length is related to these terms through the f-number or numerical aperture, defined as the focal length divided by the diameter of the aperture. Reducing the aperture size increases the f-stop, impacting light intake and depth of field in photography.

PREREQUISITES
  • Understanding of lens terminology, including "focal length" and "aperture".
  • Basic knowledge of photography concepts, specifically "f-stop" and "depth of field".
  • Familiarity with optical physics principles related to light and lenses.
  • Experience with camera settings and their effects on image capture.
NEXT STEPS
  • Research the concept of "f-number" in photography and its implications on exposure.
  • Explore how aperture settings affect depth of field in various photographic scenarios.
  • Learn about different types of lenses and their specific applications in photography.
  • Investigate the impact of lens diameter on image quality and light gathering ability.
USEFUL FOR

Photographers, optical engineers, and anyone interested in understanding the technical aspects of lens performance and photography settings.

moatasim23
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I am a bit of confused with the following terms involved in the study of lenses:
Diameter of lens
Aperture of Lens
Are these terms synonomous?
And how are they related to focal length of a lens?
 
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'diameter' and 'aperture' are often interchangeable, and they are unrelated to the focal length. The ratio of focal length and diameter is given by the f-number or the numerical aperture.
 


The "diameter of a lens" is measured from one edge of the lens to the opposite, through the center. It is, in other words, just the "diameter" of the circular edge of the lens. The "aperture" is the opening that allows light through and, as a single number, refers to the diameter of that opemimg. That can be as large as the diameter of the lens but most devices using lenses, telescopes, microscopes, cameras, have a "shutter" that allows you to close off part of the lens, giving an aperture that is smaller that the physical diameter of the lense.

The "focal ratio", or "f-stop" on a camera, is the focal length of the lens divided by the diameter of the aperture. Reducing the size of the aperture increases the "f-stop".
 

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